This invention relates to an air-laydown process and apparatus for assembling textile fibers into webs and is more particularly concerned with improvements in collecting textile fibers to form webs which are suitable for use in producing high quality nonwoven fabric.
Zafiroglu U.S. Pat. No. 3,797,074 discloses a process and apparatus for high speed production of uniform webs from feed batts of staple fibers. The batt is fed into a space between a toothed disperser roll, rotating at a surface speed of at least 3,000 feet per minute, and a stationary, curved disperser plate which is closely-spaced from the disperser roll teeth to hold the fibers close to the roll until a fiber-doffing position is reached at the tip of the disperser plate. At this location the fibers are projected, by tangential ejection from the roll, through an opening into duct means. Air supply directs a stable stream of air, of uniform velocity, low turbulence and low vorticity, through the duct in the direction of movement of the roll surface so that the fibers are projected into the stream at an angle of less than about 25.degree. and preferably less than 12.degree. to the direction of air flow through the duct. The fibers are carried in the air stream to condenser means which separates the fibers from the air to form webs weighing from about 0.1 to 10 ounces per square yard as determined by the relative speeds of the fiber feed and condenser means.
The process of the above patent provides webs which are of high quality relative to webs produced by previous processes. However, the webs are still subject to basis-weight variations which show up in non-woven fabrics prepared from the webs. It has now been found that the variations are caused by non-uniformities in flow of air through the space between the disperser roll and the disperser plate. Hot wire anemometer measurements show a predominant aerodynamic pulsation in the slit between the roll and plate which is at a frequency equal to the roll speed. This air pulsation causes uniformly spaced, cross-directional lines in the web, called chatter marks. Flow vortices having axes along the roll circumference cause machine direction streaks in the web. Non-uniform fiber separation or segregation of fibers into clumps causes blotches in the web. The present invention reduces all three of these types of web variations. Furthermore, the invention provides for the production of uniform webs at higher speeds than have been possible previously. Other advantages of the invention will become apparent from the disclosure and claims.